How to create a face out of edges
You definitely need more then one face to fill that side, I used six.

The best way to fill that shape would be to look at your model, and think about what edges you need where, then decide what faces should go where. You should be thinking about edge flow, and face loops for your entire model.

In this gif I added two edges on the bottom, then by selecting two edges at a time pressing F, filled the side with new faces.